VIENNA (Reuters) - Iran and six world powers on Friday agreed to a four-month extension of negotiations on a long-term nuclear deal that would gradually end sanctions on Tehran in exchange for curbs on its nuclear programme, diplomats close to the talks said.

Iran, the United States, Britain, France, Germany, Russia and China had set a July 20 deadline to complete a long-term agreement that would resolve the decade-old dispute over Tehran's nuclear ambitions. But diplomats said they were unable to overcome significant differences on major sticking points...